1. Field of the Invention
The present invention relates to a hard coating film for a forming tool and a forming tool coated with the same. More particularly, the present invention relates to a hard coating film, for a forming tool, excellent in wear resistance and a forming tool coated with the same.
2. Description of the Related Art
It has been usual to improve the wear resistance and the seizure resistance of a forming tool, such as a forming die, by a nitriding process. Recently, studies have been made to improve the wear resistance and the seizure resistance of a forming tool by a vapor-phase coating method, such as a PVD process. A tool disclosed in, for example, JP-A 2000-144376 (Cited reference 1) is coated with a composite nitride containing at least two elements among Cr, Al, Ti and V to improve sliding performance. Surface-coated forming dies excellent in wear resistance and seizure resistance disclosed in JP-A 2002-307128 (Cited reference 2) and JP-A 2002-307129 (Cited reference 3) are coated with a nitride, a carbide and a carbonitride of at least one element among Ti, V, Al, Cr and Si, and, in some cases, coated with a film of a sulfide layer containing Ti, Cr and Mo as the rest in addition to the former film. A surface-coating material excellent in wear resistance and seizure resistance disclosed in JP-A 2000-1768 (Cited reference 4) is obtained by coating a hard nitride layer with a MoS2 layer.
Although the composite nitride containing at least two elements among Cr, Al, Ti and V disclosed in Cited reference 1 has a high hardness and is excellent in wear resistance, the composite nitride is unsatisfactory in seizure resistance. A tool coated with a film of this composite nitride cannot withstand a severe working process, such as a metal forming process that exerts high pressure on the surface of the tool. Although a nitride, a carbide and a carbonitride of at least one element among Ti, V, Al, Cr and Si disclosed in Cited reference 2 have high hardness, the same are unsatisfactory in seizure resistance. When a sulfide film is used to improve seizure resistance as mentioned in Cited references 3 and 4, the sulfide film is effective in improving sliding performance at an early stage of use. However, since the sulfide is soft, the sulfide coating wears with time of use is unsatisfactory in durability. A film excellent in sliding performance is proposed in JP-A 2006-124818. This previously proposed film contains XCM1-C(BaCbN1-a-b) [X: at least one element among 4a, 5a, 6a, Al, Si, Fe, Co and Ni, M: at least one element among V, Mo and W]. Although this film, similarly to the sulfide film, is effective in improving sliding performance at an early stage of use, this film is unsatisfactory in durability. When a ferrous base having a low hardness is coated with a film of one of a nitride, a carbide and a carbonitride of at least one element among Ti, V, Al, Cr and Si, the film tends to come off the ferrous base due to the difference in plastic deformation between the ferrous base and the film.